Portable data carriers are used for example in cashless payments, in access controls, as identification documents, etc. Many applications use portable data carriers having graphical representations. Insofar as the graphical representations are security-relevant, they should be protected against tampering. The graphical representations may be for example a photograph of the owner of the portable data carrier.
From U.S. Pat. No. 5,421,619 it is known to apply a strip of recording material for laser inscription to an identification card having a photograph of an authorized user. An image determined by processing of the photograph is inscribed by a laser beam in the recording material in proximity to the photograph.
In the known identification card the photograph and the image derived therefrom are perceived as separate graphical elements.
From DE 41 34 539 A1 there is known a recording medium with colored image information. The image information is divided up into at least two information portions which are congruently superimposed and complement each other to form the total information. The information portions are applied in separate working steps. At least one of the information portions is present so as to be inaccessible from outside. In particular, the image information is divided up into a black and white component and a color component. The black and white component is burnt into a transparent film layer of the recording medium as a grayscale image for example by a laser scriber.
The congruent superimposition of the information portions is relatively elaborate and limits the design options in representing the image information.